Machine tool

ABSTRACT

The present invention provides a machine tool capable of achieving a higher feed rate of a spindle and weight reduction while ensuring necessary stiffness of a column. The present invention includes: a bed  2;  a saddle  4  disposed on the bed  2  to be movable in a Y-axis direction in a front view of the machine; a table  5  disposed on the saddle  4  to be movable in an X-axis direction; a column  3  having a shape of a gate that is bridged over a travel range of the table  5  and has right and left legs  3   a  fixed on the bed  2  and a beam connecting tops of the right and left legs  3   a;  and a spindle head  6  disposed on a front face of the beam  3   b  to be movable in a Z-axis direction.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a machine tool that machines a workpiece while moving a vertically set spindle and the workpiece relatively to each other in X-axis, Y-axis, and Z-axis directions.

2. Discussion of the Related Art

For example, a vertical machining center that machines a workpiece using a table movable in X-axis and Y-axis directions and a spindle movable in a Z-axis direction is generally structured, as shown in FIG. 10, to include: a column 61 fixedly disposed on a back end of a fixed bed 60 when seen from a front side of the machine; a saddle 62, for placing a workpiece W thereon, disposed on a front part of the fixed bed 60 to be movable in the Y-axis direction (forward and backward direction); a table 63 disposed on the saddle 62 to be movable in the X-axis direction (right and left direction); and a spindle head 65, with a spindle 64 attached thereto, disposed on a front face of the column 61 to be movable in the Z-axis direction (vertical direction).

In some conventional vertical machining centers of this type, the stroke of the saddle 62 in the Y-axis direction is secured by the structure such that the spindle head 65 is overhung from the column 61 toward the front side by a Y-axis stroke amount.

Further, in some cases, a tool magazine 66 of an automatic tool changer is disposed on a side face of the column 61 for replacing a preceding working tool T attached to the spindle 64 by a subsequent working tool housed in the tool magazine 66.

The above-described vertical machining center can also sometimes include a workpiece changer for replacing a machined workpiece by a subsequent machined workpiece. In this case, the use of a turn-type workpiece changer can shorten the workpiece replacement time. This turn-type workpiece changer is disposed on a front side of the machine (an operator's side).

SUMMARY OF THE INVENTION

When the spindle is overhung from the column in the Y-axis direction as in the above-described conventional machine, an excessive bending moment is generated in the column especially at the acceleration/deceleration time of the spindle head. This imposes the limit on the allowable acceleration/deceleration speed of the spindle head, resulting in a limited feed rate. There is a demand for solution to this problem in order to realize productivity improvement.

Another problem of the above-described conventional machine, in which the tool magazine is disposed on the side face of the column, is that the width dimension of the machine is naturally increased.

The above-described structure of disposing the workpiece changer on the front side of the machine as described above poses a concern that an operator may have difficulty in accessing the spindle, namely, a concern about poor approachability, resulting in lowered work efficiency of maintenance and the like.

It is an object of the present invention to provide a machine tool that is capable of achieving a higher feed rate of a spindle head and weight reduction while ensuring necessary stiffness of a column.

It is another object of the present invention to provide a machine tool whose width dimension is not increased even when it includes a tool magazine.

It is still another object of the present invention to provide a machine tool capable of enhancing approachability to a spindle to improve work efficiency even when it includes a workpiece changer.

In a first invention, a machine tool includes: a bed; a saddle disposed on the bed to be movable in a forward and backward (Y-axis) direction in a front view of the machine tool; a table disposed on the saddle to be movable in a right and left (X-axis) direction; a column in a gate shape that is bridged over a travel range of the table and has right and left legs fixed on the bed and a beam connecting tops of the right and left legs; and a spindle head disposed on a front face of the beam to support a spindle and movable in a vertical (Z-axis) direction.

In the first invention, the column in the gate shape is disposed on the bed to be bridged over the travel range of the table with the beam connecting the tops of the right and left legs, which allows the table to move in the X-axis and Y-axis directions under the column. This structure achieves the arrangement of the spindle head on the column without any overhang or with the minimum overhang. As a result, it is possible to increase an allowable acceleration/deceleration value of the spindle head, so that the feed rate can be increased. This can improve productivity in accordance with the shortened machining time.

Further, owing to the minimized overhang amount of the spindle head, the influence to machining accuracy can be eliminated and stiffness of the column need not be strengthened more than necessary, which realizes weight reduction of the structure.

In a preferable embodiment of the first invention, the beam of the column is displaced from the right and left legs toward a back face side of the machine tool, and an axis of the spindle head substantially coincides with centers of the legs in a side view of the machine tool.

In the above-described embodiment, the beam of the column is displaced from the right and left legs toward the back face side of the machine tool and the axis of the spindle head substantially coincides with the centers of the legs, so that the overhang of the spindle head from the right and left legs can be minimized or eliminated. This can further increase the allowable acceleration/deceleration value of the spindle head, so that the feed rate can be further increased.

In another preferable embodiment of the first invention, the beam of the column is set above the bed at a substantially center portion of the bed in terms of the Y-axis direction.

In the above-described embodiment, the beam is set above the bed substantially at the center portion of the bed in terms of the Y-axis direction, so that a Y-axis direction dimension of the bed can be set substantially equal to a Y-axis stroke amount of the table. Accordingly, the overall machine tool can be made compact compared with the conventional one in which the column is disposed at the back end of the bed.

In still another preferable embodiment of the first invention, the right and left legs of the column are inclined with upper portions thereof being positioned closer to the spindle.

In the above-described embodiment, the right and left legs are inclined with the upper portions thereof being positioned closer to the spindle, so that it is possible to shorten an X-axis direction length of the beam. Accordingly, the overall column can have higher stiffness and can be made compact.

In yet another preferable embodiment of the first invention, the bed has vertical walls on which the right and left legs are fixedly mounted and which have recessions recessed outward in right and left directions, and the machine tool further includes an X-axis guide rail guiding the table in the X-axis direction, ends of the X-axis guide rail being positioned in the recessions.

In the above-described embodiment, the ends of the X-axis guide rail are positioned in the recessions of the vertical walls of the bed, so that it is possible to suppress the increase in width dimension of the machine tool body while securing an X-axis direction travel amount of the table.

In a second invention, a machine tool includes: a bed; a saddle disposed on the bed to be movable in a forward and backward (Y-axis) direction in a front view of the machine tool; a table disposed on the saddle to be movable in right and left (X-axis) direction; a column fixed on the bed; a spindle head disposed on the column to support a spindle and movable in a vertical (Z-axis) direction; an automatic tool changer disposed on a back face side of the column, wherein the column has an opening which allows the back face side and a front face side of the column to communicate with each other, and the automatic tool changer replaces a tool on the spindle side by a tool on a tool magazine side through the opening.

In the second invention, the automatic tool changer is disposed on the back face side of the column and it replaces the tool on the spindle side by the tool on the tool magazine side through the opening allowing the back face side and the front face side of the column to communicate with each other, so that it is possible to utilize a vacant space on the back face of the column for disposing the tool magazine. This can prevent the increase in the width dimension of the machine.

In a preferable embodiment of the second invention, the column has a shape of a gate that is bridged over a travel range of the table and has right and left legs and a beam connecting tops of the right and left legs, and the automatic tool changer is disposed on a back face side of the beam of the column and passes under a lower edge of the beam to replace the tool on the spindle side by the tool on the tool magazine side.

In the above-described embodiment, the column has the shape of the gate bridged over the travel range of the table with the beam connecting the tops of the right and left legs, so that it is possible to effectively utilize, for tool replacement, a machining opening under the column tool. This eliminates the need for separately saving a space for tool replacement, so that the overall machine tool can be made compact.

In another preferable embodiment of the second invention, the beam of the column is displaced from the right and left legs toward a back face side of the machine tool and is set above the bed at a substantially center portion of the bed in terms of the Y-axis direction.

In the above-described embodiment, since the beam of the column is displaced from the right and left legs toward the back face side of the machine tool and is set at the substantially center portion of the bed in terms of the Y-axis direction, it is possible to effectively utilize a vacant space of the back face side of the beam for disposing the tool magazine, so that the overall machine tool can be made compact.

In still another preferable embodiment of the second invention, the automatic tool changer includes: a tool magazine disposed on the back face of the beam of the column; a change arm shaft vertically passing through the beam; a change arm turnably connected to a lower end of the change arm shaft; a change arm turn driving unit connected to an upper end of the change arm shaft; and a tool transfer mechanism disposed in parallel to the change arm shaft to transfer a tool between the tool magazine and the change arm.

In the above-described embodiment, the change arm shaft is disposed to vertically pass through the beam and the tool transfer mechanism is disposed in parallel to the change arm shaft, so that it is possible to dispose a tool change unit on the back face side of the beam with reduced installation space necessary.

In a third invention, a machine tool includes: a bed; a saddle disposed on the bed to be movable in a forward and backward (Y-axis) direction in a front view of the machine tool; a table disposed on the saddle to be movable in a right and left (X-axis) direction; a column having a shape of a gate bridged over a travel range of the table and fixed on the bed; a spindle head disposed on the column to support a spindle and movable in a vertical (Z-axis) direction; a workpiece changer that turns a workpiece together with a pallet or independently turns the workpiece, for workpiece replacement, between a workpiece standby position set on a back face side of the bed and the table placed at a workpiece change position, the workpiece changer being disposed so as to set the workpiece change position at a position under the column.

In the third invention, the column has the shape of the gate bridged over the travel range of the table, the workpiece standby position is set on the back face side of the bed, and the workpiece change position is set under the column, so that it is possible to dispose the turn-type workpiece changer on the back face side of the bed through the use of an opening under the column. This realizes easy approachability to the spindle from a front side of the bed, resulting in improved work efficiency of maintenance.

In a preferable embodiment of the third invention, the column has right and left legs and a beam connecting tops of the right and left legs to be formed in the gate shape.

In the above-described embodiment, the column is in the gate shape with the beam connecting the tops of the right and left legs. Therefore, it is possible to effectively utilize a machining opening under the column for disposing the workpiece changer, so that the overall machine tool can be made compact.

In another preferable embodiment of the third invention, the beam of the column is displaced from the right and left legs toward a back face side of the machine tool and is positioned at a substantially center portion of the bed in terms of the Y-axis direction.

In the above-described embodiment, the beam is displaced from the right and left legs toward the back face side of the machine tool and is positioned at the substantially center portion of the bed in terms of the Y-axis direction, so that it is possible to secure a turn space for workpiece replacement on the bed and to further enhance approachability to the spindle from the front side of the bed.

In still another preferable embodiment of the third invention, the machine tool further includes a turn shaft disposed on the back face side of the bed and turning the pallet or the workpiece, wherein the workpiece standby position is set outside the machine tool on the back face side of the bed and the workpiece change position is set under the column.

In the above-described embodiment, the workpiece standby position is set outside the machine on the back face side of the bed and the turn shaft is disposed on the back face side of the bed, which can facilitate a workpiece attaching/detaching operation and prevent the increase in installation area of the workpiece changer.

BRIEF DESCRIPTION OF THE DRAWINGS

The structure, operation, and effect of the present invention will be detailed in an embodiment based on the following attached drawings.

FIG. 1 is a front view to explain a vertical machining center according to an embodiment of the present invention;

FIG. 2 is a right side view of the vertical machining center;

FIG. 3 s a plane view of the vertical machining center;

FIG. 4 is a rear perspective view of the vertical machining center;

FIG. 5 is a rear view of the vertical machining center;

FIG. 6 is a left side view of the vertical machining center;

FIG. 7 is a side view showing the structure of a tool changer provided in the vertical machining center;

FIG. 8 is a schematic perspective view of a workpiece changer of the vertical machining center;

FIG. 9 is a schematic side view of the workpiece changer; and

FIG. 10 is a schematic view of a typical vertical machining center of a conventional art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention will be hereinafter described based on the attached drawings.

FIG. 1 to FIG. 7 show a vertical machining center 1. The machining center 1 includes a gate-shaped column 3 fixed on a substantially center portion of a fixed bed 2 in terms of a forward and backward direction, a saddle 4 disposed under the column 3 to be movable in a Y-axis (forward and backward) direction, a table 5 disposed on the saddle 4 to be movable in an X-axis (right and left) direction, and a spindle head 6 disposed on a front face of the column 3 to be movable in a Z-axis (vertical) direction. A spindle 7 is rotatably supported by a lower end of the spindle head 6, and a tool T is detachably attached to the spindle 7.

In the vertical machining center 1 described above, a workpiece (not shown) placed on the table 5 is cut by the tool T while the workpiece and the spindle 7 are moved relatively to each other, the workpiece moving in the X-axis and Y-axis directions and the spindle 7 moving in the Z-axis direction.

On a back face side of the fixed bed 2, mounted is a workpiece changer 12 that turns 180 degrees a preceding process pallet P1 on which a machined workpiece is placed and a subsequent process pallet P2 on which a subsequently machined workpiece is placed, via a turn shaft 37, thereby automatically replacing these pallets P1, P2. Further, a chip disposer 13 is provided on a bottom of the fixed bed 2. The chip disposer 13 includes a conveyor 47 and a coolant tank 48, the conveyor 47 collecting a cutting fluid supplied to a workpiece machining portion and discharging chips produced by workpiece machining out of the machine.

The fixed bed 2 includes right and left vertical walls 2 a, 2 a, saddle supports 2 b, 2 b formed in a stepped shape inside the right and left vertical walls 2 a, and a substantially flat bottomed recession 2 c stepped down from the right and left saddle supports 2 b. This bottomed recession 2 c is positioned at a center portion of the bed 2 in terms of the X-axis direction with a back face side and an upper face side thereof opened. The right and left vertical walls 2 a on the back face side of the fixed bed 2 are coupled to each other with a cross member 8.

Right and left Y-axis guide rails 15 supportingly guiding the saddle 4 in the Y-axis direction extend along inner edges of the right and left saddle supports 2 b. Each of the Y-axis guide rails 15 includes a rail 15 a fixed to the saddle support 2 b and a guide 15 b fixed to a bottom face of the saddle 4, the rail 15 a and the guide 15 b being slidably fitted to each other.

Further, right and left Y-axis ball screws 16, 16 for driving the movement of the saddle 4 in the Y-axis direction are rotatably fixed to outer sides of the respective Y-axis guide rails 15 on the right and left saddle supports 2 b, and Y-axis drive motors 17, 17 for driving the rotation of the ball screws 16 are connected to front ends of the respective Y-axis ball screws 16.

A pair of front and back X-axis guide rails 18, 18 for supportingly guiding the table 5 in the X-axis direction are disposed on a top face of the saddle 4. Each of the X-axis guide rails 18 includes a rail 18 a fixed to the saddle 4 and a guide 18 b fixed to a bottom face of the table 5, the rail 18 a and the guide 18 b being slidably fitted to each other.

Between the front and back X-axis guide rails 18 on the top face of the saddle 4, one X-axis ball screw 19 for driving the movement of the table 5 in the X-axis direction is rotatably fixed, and an X-axis drive motor 20 for driving the rotation of the ball screw 19 is connected to a left end of the X-axis ball screw 19.

A pair of right and left Z-axis guide rails 21, 21 for supportingly guiding the spindle head 6 in the Z-axis direction is disposed on the front face of the column 3. Each of the Z-axis guide rails 21 includes a rail 21 a fixed to a back face of the spindle head 6 and a guide 21 b fixed to the front face of the column 3, the rail 21 a and the guide 21 b being slidably fitted to each other.

Right and left Z-axis ball screws 22, 22 for driving the movement of the spindle head 6 in the Z-axis direction are rotatably fixed on outer sides of the respective Z-axis guide rails 21 on the front face of the column 3, and Z-axis drive motors 23, 23 for driving the rotation of the ball screws 22 are connected to upper ends of the respective Z-axis ball screws 22.

The spindle head 6 has arms 6 a, 6 a extending in the right and left directions, and nuts 22 a fitted to the Z-axis ball screws 22 are attached to the right and left arms 6 a.

The column 3 is formed integrally by casting and has a shape of a gate that is bridged over an X-axis and Y-axis travel range of the table 5 in a front view of the machine and has right and left legs 3 a, 3 a and a beam 3 b integrally connecting tops of the right and legs 3 a. The right and left legs 3 a are fixed on top faces of the right and left vertical walls 2 a of the fixed bed 2. In this structure, a machining opening A which is opened in the Y-axis direction and whose width in the X-axis direction is wide is formed under the column 3.

In a front view of the machine, the right and left legs 3 a are inclined so that upper portions 3 d of the legs 3 a are positioned closer to the spindle head 6 and form a substantially triangular shape with the spindle head 6 side having larger vertical dimension. Further, the beam 3 b are formed in a square shape with an upper edge and an open lower edge thereof being substantially parallel to each other.

In a plane view of the machine, the column 3 is formed in a substantially arch shape so that the beam 3 b is displaced from the right and left legs 3 a, 3 a toward the back face side of the machine, and a front face 3 b′ of the beam 3 b substantially coincides with a leg center line C1 passing through the centers of the right and left legs 3 a in terms of the forward and backward direction. Further, the beam 3 b is positioned at a center of the fixed bed 2 in terms of the Y-axis direction, and the right and left legs 3 a are positioned on a front side thereof. A housing recession 3 c for housing the spindle head 6 and the right and left Z-axis ball screws 22 is formed on the front face 3 b′ of the beam 3 b. This structure eliminates the overhang of the spindle head 6 from the column 3.

Side wall recessions 2 d recessed outward in the right and left directions of the machine are formed in the right and left vertical walls 2 a of the bed 2 respectively. Ends 18 c of the X-axis guide rails 18 are positioned in the right and left side wall recessions 2 d respectively.

A tool changer 10 for automatically replacing a preceding working tool T attached to the spindle 7 by a subsequent working tool T1 attached to the tool magazine 11 through the opening A of the column 3 is mounted on the column 3.

The tool changer 10 includes: the tool magazine 11 in a circular shape that vertically holds a large number of tools Tn by a pot with the tools Tn facing downward and drives the turn of the subsequent working tool T1 for indexing at a tool indexing position “a”; a tool transfer mechanism 25 that transfers the subsequent working tool T1 indexed at the indexing position “a” to a tool change position “b” and returns the preceding working tool T, which is returned to the tool change position “b”, to the tool magazine 11; and a change arm 26 replacing the preceding working tool T, which is transferred to a tool change position “c” by the spindle 7, by the subsequent working tool T1 transferred to the tool change position “b”.

The tool magazine 11 is disposed on a back face 3 b″ of the beam 3 b of the column 3 and is suspendedly supported by a bracket 27 fixed to the back face 3 b″. Note that 11 a denotes a turn indexing motor.

A change arm shaft 28 is insertedly disposed on a back side of the spindle head 6 on the beam 3 b so as to vertically pass through the beam 3 b. The change arm 26 is connected to a bottom end of the change arm shaft 28, and a turn driving unit 29 for driving the change arm 26 to turn 180 degrees is connected to an upper end of the change arm shaft 28. A drive motor 30 is connected to the turn driving unit 29. A balance spring 34 constantly biases the change arm shaft 28 upward to cancel the weight of the tool.

The tool transfer mechanism 25 includes: a direct acting guide 31 disposed in a rectangular hole 3 e (see FIG. 3) formed on a back side of the change arm shaft 28 in the beam 3 b to be parallel to the change arm shaft 28; a hook 32 supported by the direct acting guide 31 to be vertically movable and gripping the pot of the subsequent working tool T1; and an air cylinder 33 for driving the hook 32 to move up/down between the tool indexing position “a” and the tool change position “b”.

The change arm 26 is kept on standby under the lower edge of the beam 3 b with its longitudinal direction aligned with the X-axis direction. Then, the change arm 26 replaces the preceding working tool T on the front face 3 b′ side of the beam 3 b by the subsequent working tool T1 on the back face 3 b″ side thereof through the opening A of the column 3.

When the workpiece machining is finished, the spindle head 6 moves in the Z-axis direction to locate the preceding working tool T at the tool change position “c”, and the tool magazine 11 turns and indexes the subsequent working tool T1 to locate it at the tool indexing position “a”. The hook 32 grips the pot of the subsequent working tool T1 indexed at the tool indexing position “a”, and the air cylinder 33 transfers the subsequent working tool T1 together with the hook 32 to the tool change position “b” to locate it at this change position “b”. The change arm 26 turns from the standby position to grip the preceding working tool T as well as the subsequent working tool T1, moves down in this state to take out the tools T, T1, turns 180 degrees, and thereafter moves up. Through this operation, the preceding working tool T is placed in a pot kept on standby at the tool change position “b”, and the subsequent working tool T1 is attached to the spindle 7. The preceding working tool T is lifted together with the hook 32 to be returned to the tool magazine 11.

The workpiece changer 12 is roughly structured such that a clamp 38 is fixed to an upper end of the turn shaft 37 disposed to be ascendible/descendible and turnable 180 degrees. The clamp 38 has grooves 38 a, 38 a fittable to hooks 39, 40 formed in the aforesaid pallets P1, P2, and hydraulic pistons 41, 41 are disposed in the respective grooves 38 a to be projectable/retreatable. When the hydraulic pistons 41 protrude into the grooves 38 a, the pallets P1, P2 are clamped and when they retreat out of the grooves 38 a, the pallets P1, P2 are unclamped.

The subsequent process pallet P2 is positioned at a workpiece standby position B that is set outside the machine on a back face side of the fixed bed 2, and the preceding process pallet P1 is positioned at a workpiece change position C that is set under the column 3. Further, the turn shaft 37 is disposed on a back end of the fixed bed 2.

A subsequent machined workpiece is placed in the subsequent process pallet P2 at the workpiece standby position B in advance. When workpiece machining is finished, the table 5 moves in the X-axis and Y-axis directions to transfer the preceding process pallet P1 to the workpiece change position C. The turn shaft 37 moves up, the hooks 39, 40 of the pallets P1, P2 are fitted in the respective grooves 38 a, and the hydraulic pistons 41 protrude to clamp the pallets P1, P2. The turn shaft 37 further moves up to lift the pallets P1, P2 from the table 5, turns 180 degrees in this state, and thereafter moves down. Through this operation, the preceding process pallet P1 and the subsequent process pallet P2 are placed at the workpiece standby position B and on the table 5 at the workpiece change position C respectively.

According to this embodiment, the column 3 is in the gate shape in which the beam 3 b connects the tops of the right and left legs 3 a, 3 a, and is fixed on the top faces of the right and left vertical walls 2 a, 2 a of the fixed bed 2, being bridged over the travel range of the table 5, which allows the table 5 to move in the X-axis and Y-axis directions through the opening A under the column 3. This enables the arrangement of the spindle shaft 6 on the column 3 without any overhang. As a result, the allowable acceleration/deceleration value of the spindle head 6 at the Z-axis direction feed time can be increased. In accordance therewith, the feed rate can be increased to shorten the machining time, resulting in improved productivity.

Moreover, since the overhang of the spindle head 6 can be eliminated, it is possible to eliminate the influence to machining accuracy and eliminate the need for increased stiffness of the column 3 more than necessary, resulting in reduced cost and weight.

Since the beam 3 b of the column 3 is positioned at the center portion of the fixed bed 2 in terms of the Y-axis direction, it is possible to set the Y-axis direction dimension of the fixed bed 2 substantially equal to the Y-axis stroke amount of the table 5. This structure can make the overall machine compact compared with the conventional structure in which the column is disposed on the back end of the bed.

Further, the beam 3 b of the column 3 is displaced toward the back face side of the machine so that the front face 3 b′ of the beam 3 b substantially coincides with the leg center line C1 of the right and left legs 3 a, 3 a, and the axis of the spindle head 6 substantially coincides with the center line C1 of the legs 3 a. This structure can eliminate the overhang of the spindle head 6 from the right and left legs 3 a. Accordingly, it is possible to further increase the allowable acceleration/deceleration value of the spindle head 6, so that the feed rate can be further increased.

Moreover, since the right and left legs 3 a are inclined so that the upper portions 3 b are positioned closer to the spindle head 6, the length in the X-axis direction of the beam 3 b can be shortened. Accordingly, the overall column can have increased stiffness and can be made compact.

Further, the ends 18 c of the respective rails 18 a of the X-axis guide rails 18 are positioned in the recessions 2 d of the vertical walls 2 a of the fixed bed 2, so that it is possible to suppress the increase in width dimension of the machine body while securing the travel amount in the X-axis direction of the table 5.

According to this embodiment, the automatic tool changer 10 is disposed on the back face 3 b″ side of the column 3 formed in the gate shape, and it replaces the preceding working tool T on the spindle 7 side by the subsequent working tool T1 on the tool magazine 11 side through the opening A that allows the back face 3 b″ side and the front face 3 b′ side of the column 3 to communicate with each other, so that the vacant space of the back face 3 b″ of the column 3 can be utilized for placing the tool magazine 11, which can prevent the increase in the width dimension of the machine.

Since the column 3 is in the gate shape bridged over the travel range of the table with the beam 3 b connecting the tops of the right and left legs 3 a, the machining opening A formed under the column 3 can be effectively utilized for tool replacement. This can eliminate the need for a tool change space and can make the overall machine compact.

Further, the beam 3 b of the column 3 is displaced from the right and left legs 3 a toward the back face side of the machine and is disposed at the center portion of the fixed bed 2 in terms of the Y-axis direction, so that the vacant space on the back face 3 b″ side of the beam 3 b can be effectively used for placing the tool magazine 11 and the overall machine can be made compact.

Moreover, the change arm shaft 28 vertically passes through the beam 3 b, and the tool transfer mechanism 25 is parallel to the change arm shaft 28, so that it is possible to dispose a tool change unit such as the change arm shaft 28 and the tool transfer mechanism 25 with reduced required arrangement space.

According to this embodiment, the column 3 is in the gate shape bridged over the travel range of the table 5, the workpiece standby position B is set outside the machine on the back face side of the fixed bed 2, and the workpiece change position C is set under the column 3. Accordingly, it is possible to utilize the machining opening A under the column 3 for arranging the turn-type workpiece changer 12 on the back face side of the fixed bed 2. This structure realizes easy approachability to the spindle 7 from the front side of the bed 2 and improved work efficiency of maintenance.

Further, the column 3 is in the gate shape with the beam 3 b connecting the tops of the right and left legs 3 a, so that it is possible to effectively utilize the machining opening A under the column 3 for disposing the workpiece changer 12, which can make the overall machine compact.

In addition, since the beam 3 b is displaced from the right and left legs 3 a toward the back face side of the machine and is positioned at the center portion of the fixed bed 2 in terms of the Y-axis direction, it is possible to secure a turn space for workpiece replacement in the center portion of the bed and to further improve approachability to the spindle 7 from the front side of the bed.

Further, the workpiece standby position B is set outside the machine on the back face side of the fixed bed 2 and the turn shaft 37 is disposed on the back end of the fixed bed 2, the workpiece attaching/detaching operation can be facilitated and the increase in installation area of the workpiece changer 12 can be suppressed.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof.

The present embodiments are therefore to be considered in all respects as illustrative and no restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. 

1: A machine tool comprising: a bed; a saddle disposed on said bed to be movable in a forward and backward (Y-axis) direction in a front view of the machine tool; a table disposed on said saddle to be movable in a right and left (X-axis) direction; a column in a gate shape that is bridged over a travel range of said table and has right and left legs fixed on said bed and a beam connecting tops of the right and left legs; and a spindle head disposed on a front face of the beam to support a spindle and movable in a vertical (Z-axis) direction. 2: The machine tool according to claim 1, wherein the beam of said column is displaced from the right and left legs toward a back face side of the machine tool, and an axis of said spindle head substantially coincides with centers of the legs in a side view of the machine tool. 3: The machine tool according to claim 1, wherein the beam of said column is set above said bed at a substantially center portion of said bed in terms of the Y-axis direction. 4: The machine tool according to claim 3, wherein the right and left legs of said column are inclined with upper portions thereof being positioned closer to said spindle. 5: The machine tool according to claim 1, wherein said bed has vertical walls on which the right and left legs are fixedly mounted and which have recessions recessed outward in right and left directions, and the machine tool further comprising: an X-axis guide rail guiding said table in the X-axis direction, ends of the X-axis guide rails being positioned in the recessions. 6: A machine tool comprising: a bed; a saddle disposed on said bed to be movable in a forward and backward (Y-axis) direction in a front view of the machine tool; a table disposed on said saddle to be movable in right and left (X-axis) direction; a column fixed on said bed; a spindle head disposed on said column to support a spindle and movable in a vertical (Z-axis) direction; an automatic tool changer disposed on a back face side of said column, wherein said column has an opening which allows the back face side and a front face side of said column to communicate with each other, and wherein said automatic tool changer replaces a tool on said spindle side by a tool on a tool magazine side through the opening. 7: The machine tool according to claim 6, wherein said column has a shape of a gate that is bridged over a travel range of said table and has right and left legs and a beam connecting tops of the right and left legs, and wherein said automatic tool changer is disposed on a back face side of the beam of said column and passes under a lower edge of the beam to replace the tool on said spindle side by the tool on the tool magazine side. 8: The machine tool according to claim 7, wherein the beam of said column is displaced from the right and left legs toward a back face side of the machine tool and is set above said bed at a substantially center portion of said bed in terms of the Y-axis direction. 9: The machine tool according to claim 7, wherein said automatic tool changer includes: a tool magazine disposed on the back face of the beam of said column; a change arm shaft vertically passing through the beam; a change arm turnably connected to a lower end of the change arm shaft; a change arm turn driving unit connected to an upper end of the change arm shaft; and a tool transfer mechanism disposed in parallel to the change arm shaft to transfer a tool between the tool magazine and the change arm. 10: A machine tool comprising, a bed; a saddle disposed on said bed to be movable in a forward and backward (Y-axis) direction in a front view of the machine; a table disposed on said saddle to be movable in a right and left (X-axis) direction; a column in a gate shape bridged over a travel range of said table and fixed on said bed; a spindle head disposed on said column to support a spindle and movable in a vertical (Z-axis) direction; a workpiece changer that turns a workpiece together with a pallet or independently turns the workpiece, for workpiece replacement, between a workpiece standby position set on a back face side of said bed and said table placed at a workpiece change position, the workpiece changer being disposed so as to set the workpiece change position at a position under the column. 11: The machine tool according to claim 10, wherein said column has right and left legs and a beam connecting tops of the right and left legs to be formed in the gate shape. 12: The machine tool according to claim 11, wherein the beam of said column is displaced from the right and left legs toward a back face side of the machine and is positioned at a substantially center portion of said bed in terms of the Y-axis direction. 13: The machine tool according to claim 10, further comprising: a turn shaft disposed on the back face side of the bed and turning the pallet or the workpiece, wherein the workpiece standby position is set outside the machine on the back face side of said bed and the workpiece change position is set under said column. 14: The machine tool according to claim 2, wherein the beam of said column is set above said bed at a substantially center portion of said bed in terms of the Y-axis direction. 15: The machine tool according to claim 14, wherein the right and left legs of said column are inclined with upper portions thereof being positioned closer to said spindle. 16: The machine tool according to claim 2, wherein said bed has vertical walls on which the right and left legs are fixedly mounted and which have recessions recessed outward in right and left directions, and the machine tool further comprising: an X-axis guide rail guiding said table in the X-axis direction, ends of the X-axis guide rails being positioned in the recessions. 17: The machine tool according to claim 8, wherein said automatic tool changer includes: a tool magazine disposed on the back face of the beam of said column; a change arm shaft vertically passing through the beam; a change arm turnably connected to a lower end of the change arm shaft; a change arm turn driving unit connected to an upper end of the change arm shaft; and a tool transfer mechanism disposed in parallel to the change arm shaft to transfer a tool between the tool magazine and the change arm. 18: The machine tool according to claim 11, further comprising: a turn shaft disposed on the back face side of the bed and turning the pallet or the workpiece, wherein the workpiece standby position is set outside the machine on the back face side of said bed and the workpiece change position is set under said column. 19: The machine tool according to claim 12, further comprising: a turn shaft disposed on the back face side of the bed and turning the pallet or the workpiece, wherein the workpiece standby position is set outside the machine on the back face side of said bed and the workpiece change position is set under said column. 